30 research outputs found
Photon-pair generation by non-instantaneous spontaneous four-wave mixing
We present a general model, based on a Hamiltonian approach, for the joint
quantum state of photon pairs generated through pulsed spontaneous four-wave
mixing, including nonlinear phase-modulation and a finite material response
time. For the case of a silica fiber, it is found that the pair-production rate
depends weakly on the waveguide temperature, due to higher-order Raman
scattering events, and more strongly on pump-pair frequency detuning. From the
analytical model, a numerical scheme is derived, based on the well-known
split-step method. This scheme allows computation of joint states where
nontrivial effects are included, such as group-velocity dispersion and Raman
scattering. In this work, the numerical model is used to study the impact of
the non-instantaneous response on the pre-filtering purity of heralded single
photons. We find that for pump pulses shorter than 1 ps, a significant
detuning-dependent change in quantum-mechanical purity may be observed in
silica
Engineering spectrally unentangled photon pairs from nonlinear microring resonators through pump manipulation
The future of integrated quantum photonics relies heavily on the ability to
engineer refined methods for preparing the quantum states needed to implement
various quantum protocols. An important example of such states are
quantum-correlated photon pairs, which can be efficiently generated using
spontaneous nonlinear processes in integrated microring-resonator structures.
In this work, we propose a method for generating spectrally unentangled photon
pairs from a standard microring resonator. The method utilizes interference
between a primary and a delayed secondary pump pulse to effectively increase
the pump spectral width inside the cavity. This enables on-chip generation of
heralded single photons with state purities in excess of 99 % without spectral
filtering.Comment: 5 pages, 5 figure
Spectrally pure heralded single photons by spontaneous four-wave mixing in a fiber: reducing impact of dispersion fluctuations
We model the spectral quantum-mechanical purity of heralded single photons
from a photon-pair source based on nondegenerate spontaneous four-wave mixing
taking the impact of distributed dispersion fluctuations into account. The
considered photon-pair-generation scheme utilizes pump-pulse walk-off to
produce pure heralded photons and phase matching is achieved through the
dispersion properties of distinct spatial modes in a few-mode silica step-index
fiber. We show that fiber-core-radius fluctuations in general severely impact
the single-photon purity. Furthermore, by optimizing the fiber design we show
that generation of single photons with very high spectral purity is feasible
even in the presence of large core-radius fluctuations. At the same time,
contamination from spontaneous Raman scattering is greatly mitigated by
separating the single-photon frequency by more than 32 THz from the pump
frequency
Shape-preserving and unidirectional frequency conversion using four-wave mixing Bragg scattering
In this work, we investigate the properties of four-wave mixing Bragg
scattering in a configuration that employs orthogonally polarized pumps in a
birefringent waveguide. This configuration enables a large signal conversion
bandwidth, and allows strongly unidirectional frequency conversion as undesired
Bragg-scattering processes are suppressed by waveguide birefringence. Moreover,
we show that this form of four-wave mixing Bragg scattering preserves the
(arbitrary) signal pulse shape, even when driven by pulsed pumps.Comment: 11 pages + refs, 5 figure
Volatile and Organic Compositions of Sedimentary Rocks in Yellowknife Bay, Gale crater, Mars
H₂O, CO₂, SO₂, O₂, H₂, H₂S, HCl, chlorinated hydrocarbons, NO and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H₂O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO₂. Concurrent evolution of O₂ and chlorinated hydrocarbons suggest the presence of oxychlorine phase(s). Sulfides are likely sources for S-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic C sources may be preserved in the mudstone; however, the C source for the chlorinated hydrocarbons is not definitively of martian origin
A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars
The Curiosity rover discovered fine-grained sedimentary rocks, inferred to represent an ancient lake, preserve evidence of an environment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference N and P are assumed to have been available. The environment likely had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars
The Petrochemistry of Jake_M: A Martian Mugearite
“Jake_M,” the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the
Curiosity rover, differs substantially in chemical composition from other known martian igneous
rocks: It is alkaline (>15% normative nepheline) and relatively fractionated. Jake_M is
compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and
continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been
produced by extensive fractional crystallization of a primary alkaline or transitional magma at
elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that
alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter
even more fractionated alkaline rocks (for example, phonolites and trachytes)
Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars
Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from approximately average Martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved indicating arid, possibly cold, paleoclimates and rapid erosion/deposition. Absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature, circum-neutral pH, rock-dominated aqueous conditions. High spatial resolution analyses of diagenetic features, including concretions, raised ridges and fractures, indicate they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components and hydrated calcium-sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. Geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early
history of Mars
X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater
The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian
bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray
diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite,
and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite.
The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight
percent x-ray amorphous material, likely containing multiple Fe^(3+)- and volatile-bearing phases,
including possibly a substance resembling hisingerite. The crystalline component is similar to
the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian
basaltic meteorites. The amorphous component is similar to that found on Earth in places
such as soils on the Mauna Kea volcano, Hawaii